Exception-robust time-averaged radio frequency exposure compliance continuity

ABSTRACT

Certain aspects of the present disclosure provide techniques for exception-robust time-averaged radio frequency (RF) exposure compliance continuity. A method that may be performed by a user equipment (UE) generally includes transmitting a first signal at a first transmission power based on time-averaged RF exposure measurements over a time window and storing RF exposure information associated with the time window. The method may also include detecting that an exception event associated with the UE occurred and transmitting a second signal at a second transmission power based at least in part on the stored RF exposure information in response to the detection of the event.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present Application for Patent claims priority to U.S. ProvisionalApplication No. 63/077,377, filed Sep. 11, 2020, which is herebyexpressly incorporated by reference herein in its entirety.

BACKGROUND Field of the Disclosure

Aspects of the present disclosure relate to wireless communications, andmore particularly, to techniques for providing radio frequency (RF)exposure compliance continuity.

Description of Related Art

Wireless communication systems are widely deployed to provide varioustelecommunication services such as telephony, video, data, messaging,broadcasts, etc. Modern wireless communication devices (such as cellulartelephones) are generally required to meet radio frequency (RF) exposurelimits set by domestic and international standards and regulations. Toensure compliance with the standards, such devices must currentlyundergo an extensive certification process prior to being shipped tomarket. To ensure that a wireless communication device complies with anRF exposure limit, techniques have been developed to enable the wirelesscommunication device to assess RF exposure from the wirelesscommunication device in real time and adjust the transmission power ofthe wireless communication device accordingly to comply with the RFexposure limit.

SUMMARY

The systems, methods, and devices of the disclosure each have severalaspects, no single one of which is solely responsible for its desirableattributes. Without limiting the scope of this disclosure as expressedby the claims which follow, some features will now be discussed briefly.After considering this discussion, and particularly after reading thesection entitled “Detailed Description” one will understand how thefeatures of this disclosure provide advantages that include ensuringcompliance with radio frequency exposure limits after various exceptionevents.

Certain aspects of the subject matter described in this disclosure canbe implemented in a method for wireless communication by a userequipment (UE). The method generally includes transmitting a firstsignal at a first transmission power based on time-averaged radiofrequency (RF) exposure measurements over a time window and storing RFexposure information associated with the time window. The method mayalso include detecting that an exception event associated with the UEoccurred and transmitting a second signal at a second transmission powerbased at least in part on the stored RF exposure information in responseto the detection of the event.

Certain aspects of the subject matter described in this disclosure canbe implemented in an apparatus for wireless communication. The apparatusgenerally includes a transmitter, a memory, and a processor. Thetransmitter is configured to transmit a first signal at a firsttransmission power based on time-averaged RF exposure measurements overa time window. The processor is coupled to the memory, such that theprocessor and the memory are configured to store RF exposure informationassociated with the time window, and detect that an exception eventassociated with the apparatus occurred. The transmitter is furtherconfigured to transmit a second signal at a second transmission powerbased at least in part on the stored RF exposure information in responseto the detection of the event.

Certain aspects of the subject matter described in this disclosure canbe implemented in an apparatus for wireless communication. The apparatusgenerally includes means for transmitting a first signal at a firsttransmission power based on time-averaged RF exposure measurements overa time window; means for storing RF exposure information associated withthe time window; means for detecting that an exception event associatedwith the apparatus occurred; and means for transmitting a second signalat a second transmission power based at least in part on the stored RFexposure information in response to the detection of the event.

Certain aspects of the subject matter described in this disclosure canbe implemented in a computer-readable medium having instructions storedthereon for transmitting a first signal at a first transmission powerbased on time-averaged RF exposure measurements over a time window;storing RF exposure information associated with the time window;detecting that an exception event associated with the UE occurred; andtransmitting a second signal at a second transmission power based atleast in part on the stored RF exposure information in response to thedetection of the event.

Certain aspects of the subject matter described in this disclosure canbe implemented in a method for wireless communication by a UE. Themethod generally includes transmitting a first signal at a firsttransmission power based on time-averaged RF exposure measurements overa time window; storing RF exposure information associated with the timewindow; detecting that an exception event associated with the UEoccurred; determining that a timestamp corresponding to a most recenttime-averaged RF exposure measurement is not within a current timewindow or determining that a check value does not pass a cyclicredundancy check (CRC) of the RF exposure information; and transmittinga second signal at a second transmission power in a failsafe mode basedon the determining.

To the accomplishment of the foregoing and related ends, the one or moreaspects comprise the features hereinafter fully described andparticularly pointed out in the claims. The following description andthe appended drawings set forth in detail certain illustrative featuresof the one or more aspects. These features are indicative, however, ofbut a few of the various ways in which the principles of various aspectsmay be employed.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above-recited features of the presentdisclosure can be understood in detail, a more particular description,briefly summarized above, may be had by reference to aspects, some ofwhich are illustrated in the drawings. It is to be noted, however, thatthe appended drawings illustrate only certain typical aspects of thisdisclosure and are therefore not to be considered limiting of its scope,for the description may admit to other equally effective aspects.

FIG. 1 is a block diagram conceptually illustrating an example wirelesscommunication network, in accordance with certain aspects of the presentdisclosure.

FIG. 2 is a block diagram conceptually illustrating a design of anexample a base station (BS) and user equipment (UE), in accordance withcertain aspects of the present disclosure.

FIG. 3 is a block diagram of an example radio frequency (RF)transceiver, in accordance with certain aspects of the presentdisclosure.

FIG. 4 is a flow diagram illustrating example operations for wirelesscommunication by a UE, in accordance with certain aspects of the presentdisclosure.

FIG. 5 is a diagram illustrating time-averaged RF exposure over a timewindow, in accordance with certain aspects of the present disclosure.

FIG. 6 is a block diagram illustrating a design of an example wirelesscommunication device implementing RF exposure continuity, in accordancewith certain aspects of the present disclosure.

FIG. 7 is a signaling flow diagram illustrating example signaling for RFexposure continuity, in accordance with aspects of the presentdisclosure.

FIG. 8 illustrates a communications device (e.g., a UE) that may includevarious components configured to perform operations for the techniquesdisclosed herein in accordance with aspects of the present disclosure.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. It is contemplated that elements disclosed in one aspectmay be beneficially utilized on other aspects without specificrecitation.

DETAILED DESCRIPTION

Aspects of the present disclosure provide apparatus, methods, processingsystems, and computer-readable mediums for controlling radio frequency(RF) exposure after an exception event (such as an error, reset, crash,or reboot affecting the operations of a user equipment (UE) or a modemof the UE, or an event which results in a portion of time during whichexposure is unknown or indeterminate or detection thereof). In certainaspects, a UE may periodically store RF exposure information (such astime-averaged RF exposure measurements of the transmit power history) inmemory, preferably resistant to corruption from an exception event. Whenan exception event occurs (such as the UE rebooting or the UE's modemresetting, or the UE determining that a portion of time has elapsedduring which exposure is unknown or indeterminate), the UE may use thestored RF exposure information to determine a transmit power incompliance with the RF exposure limit. The techniques for providing RFexposure continuity described herein may enable the UE to remain incompliance with the RF exposure limits without potentially exposing auser to excessive RF fields after the UE encounters an exception event.In other words, the techniques for providing RF exposure continuitydescribed herein may provide safe operating conditions in terms of RFexposure for the user after an exception event. The techniques forproviding RF exposure continuity described herein may provide alow-power solution that consumes an acceptable amount of power to storethe RF exposure information without significantly affecting the batterylife of the UE.

The following description provides examples of RF exposure compliancemanagement in communication systems, and is not limiting of the scope,applicability, or examples set forth in the claims. Changes may be madein the function and arrangement of elements discussed without departingfrom the scope of the disclosure. Various examples may omit, substitute,or add various procedures or components as appropriate. For instance,the methods described may be performed in an order different from thatdescribed, and various steps may be added, omitted, or combined. Also,features described with respect to some examples may be combined in someother examples. For example, an apparatus may be implemented or a methodmay be practiced using any number of the aspects set forth herein. Inaddition, the scope of the disclosure is intended to cover such anapparatus or method which is practiced using other structure,functionality, or structure and functionality in addition to, or otherthan, the various aspects of the disclosure set forth herein. It shouldbe understood that any aspect of the disclosure disclosed herein may beembodied by one or more elements of a claim. The word “exemplary” isused herein to mean “serving as an example, instance, or illustration.”Any aspect described herein as “exemplary” is not necessarily to beconstrued as preferred or advantageous over other aspects.

In general, any number of wireless networks may be deployed in a givengeographic area. Each wireless network may support a particular radioaccess technology (RAT) and may operate on one or more frequencies. ARAT may also be referred to as a radio technology, an air interface,etc. A frequency may also be referred to as a carrier, a subcarrier, afrequency channel, a tone, a subband, etc. Each frequency may support asingle RAT in a given geographic area in order to avoid interferencebetween wireless networks of different RATs, and/or may be associatedwith several RATs.

The techniques described herein may be used for various wirelessnetworks and radio technologies. While aspects may be described hereinusing terminology commonly associated with 3G, 4G, and/or new radio(e.g., 5G NR) wireless technologies, aspects of the present disclosurecan be applied in other generation-based communication systems and/orpursuant to other radio technologies (e.g., 802.11, Bluetooth, etc.).

NR access may support various wireless communication services, such asenhanced mobile broadband (eMBB) targeting wide bandwidth (e.g., 80 MHzor beyond), millimeter wave (mmW) targeting high carrier frequency(e.g., 24 GHz to 53 GHz or beyond), massive machine type communicationsMTC (mMTC) targeting non-backward compatible MTC techniques, and/ormission critical targeting ultra-reliable low-latency communications(URLLC). These services may include latency and reliabilityrequirements. These services may also have different transmission timeintervals (TTI) to meet respective quality of service (QoS)requirements. In addition, these services may co-exist in the samesubframe. NR supports beamforming and beam direction may be dynamicallyconfigured. MIMO transmissions with precoding may also be supported, asmay multi-layer transmissions. Aggregation of multiple cells may besupported.

FIG. 1 illustrates an example wireless communication network 100 inwhich aspects of the present disclosure may be performed. For example,the wireless communication network 100 may be an NR system (e.g., a 5GNR network), an Evolved Universal Terrestrial Radio Access (E-UTRA)system (e.g., a 4G network), a Universal Mobile TelecommunicationsSystem (UMTS) (e.g., a 2G/3G network), or a code division multipleaccess (CDMA) system (e.g., a 2G/3G network), or may be configured forcommunications according to an IEEE standard such as one or more of the802.11 standards, etc. As shown in FIG. 1 , the UE 120 a includes an RFexposure manager 122 that provides RF exposure continuity (e.g., afteran exception event), in accordance with aspects of the presentdisclosure.

As illustrated in FIG. 1 , the wireless communication network 100 mayinclude a number of BSs 110 a-z (each also individually referred toherein as BS 110 or collectively as BSs 110) and other network entities.A BS 110 may provide communication coverage for a particular geographicarea, sometimes referred to as a “cell”, which may be stationary or maymove according to the location of a mobile BS 110. In some examples, theBSs 110 may be interconnected to one another and/or to one or more otherBSs or network nodes (not shown) in wireless communication network 100through various types of backhaul interfaces (e.g., a direct physicalconnection, a wireless connection, a virtual network, or the like) usingany suitable transport network. In the example shown in FIG. 1 , the BSs110 a, 110 b and 110 c may be macro BSs for the macro cells 102 a, 102 band 102 c, respectively. The BS 110 x may be a pico BS for a pico cell102 x. The BSs 110 y and 110 z may be femto BSs for the femto cells 102y and 102 z, respectively. ABS may support one or multiple cells.

The BSs 110 communicate with UEs 120 a-y (each also individuallyreferred to herein as UE 120 or collectively as UEs 120) in the wirelesscommunication network 100. The UEs 120 (e.g., 120 x, 120 y, etc.) may bedispersed throughout the wireless communication network 100, and each UE120 may be stationary or mobile. Wireless communication network 100 mayalso include relay stations or repeaters (e.g., relay station 110 r),also referred to as relays or the like, that receive a transmission ofdata and/or other information from an upstream station (e.g., a BS 110 aor a UE 120 r) and sends a transmission of the data and/or otherinformation to a downstream station (e.g., a UE 120 or a BS 110), orthat relays transmissions between UEs 120, to facilitate communicationbetween devices.

A network controller 130 may be in communication with a set of BSs 110and provide coordination and control for these BSs 110 (e.g., via abackhaul). In certain cases, the network controller 130 may include acentralized unit (CU) and/or a distributed unit (DU), for example, in a5G NR system. In aspects, the network controller 130 may be incommunication with a core network 132 (e.g., a 5G Core Network (5GC)),which provides various network functions such as Access and MobilityManagement, Session Management, User Plane Function, Policy ControlFunction, Authentication Server Function, Unified Data Management,Application Function, Network Exposure Function, Network RepositoryFunction, Network Slice Selection Function, etc.

FIG. 2 illustrates example components of BS 110 a and UE 120 a (e.g.,the wireless communication network 100 of FIG. 1 ), which may be used toimplement aspects of the present disclosure.

At the BS 110 a, a transmit processor 220 may receive data from a datasource 212 and control information from a controller/processor 240. Thecontrol information may be for the physical broadcast channel (PBCH),physical control format indicator channel (PCFICH), physical hybrid ARQindicator channel (PHICH), physical downlink control channel (PDCCH),group common PDCCH (GC PDCCH), etc. The data may be for the physicaldownlink shared channel (PDSCH), etc. A medium access control(MAC)-control element (MAC-CE) is a MAC layer communication structurethat may be used for control command exchange between wireless nodes.The MAC-CE may be carried in a shared channel such as a physicaldownlink shared channel (PDSCH), a physical uplink shared channel(PUSCH), or a physical sidelink shared channel (PSSCH).

The processor 220 may process (e.g., encode and symbol map) the data andcontrol information to obtain data symbols and control symbols,respectively. The transmit processor 220 may also generate referencesymbols, such as for the primary synchronization signal (PSS), secondarysynchronization signal (SSS), PBCH demodulation reference signal (DMRS),and channel state information reference signal (CSI-RS). A transmit (TX)multiple-input multiple-output (MIMO) processor 230 may perform spatialprocessing (e.g., precoding) on the data symbols, the control symbols,and/or the reference symbols, if applicable, and may provide outputsymbol streams to the modulators (MODs) in transceivers 232 a-232 t.Each modulator transceivers 232 a-232 t may process a respective outputsymbol stream (e.g., for OFDM, etc.) to obtain an output sample stream.Each modulator may further process (e.g., convert to analog, amplify,filter, and upconvert) the output sample stream to obtain a downlinksignal. Downlink signals from modulators transceivers 232 a-232 t may betransmitted via the antennas 234 a-234 t, respectively.

At the UE 120 a, the antennas 252 a-252 r may receive the downlinksignal(s) from the BS 110 a and may provide received signal(s) to thedemodulators (DEMODs) in transceivers 254 a-254 r, respectively. Eachdemodulator in transceivers 254 a-254 r may condition (e.g., filter,amplify, downconvert, and digitize) a respective received signal toobtain input samples. Each demodulator may further process the inputsamples (e.g., for OFDM, etc.) to obtain received symbols. A MIMOdetector 256 may obtain received symbols from all the demodulators intransceivers 254 a-254 r, perform MIMO detection on the received symbolsif applicable, and provide detected symbols. A receive processor 258 mayprocess (e.g., demodulate, deinterleave, and decode) the detectedsymbols, provide decoded data for the UE 120 a to a data sink 260, andprovide decoded control information to a controller/processor 280.

On the uplink, at UE 120 a, a transmit processor 264 may receive andprocess data (e.g., for the physical uplink shared channel (PUSCH)) froma data source 262 and control information (e.g., for the physical uplinkcontrol channel (PUCCH) from the controller/processor 280. The transmitprocessor 264 may also generate reference symbols for a reference signal(e.g., for the sounding reference signal (SRS)). The symbols from thetransmit processor 264 may be precoded by a TX MIMO processor 266 ifapplicable, further processed by the modulators (MODs) in transceivers254 a-254 r (e.g., for SC-FDM, etc.), and transmitted to the BS 110 a.At the BS 110 a, the uplink signal(s) from the UE 120 a may be receivedby the antennas 234, processed by the modulators in transceivers 232a-232 t, detected by a MIMO detector 236 if applicable, and furtherprocessed by a receive processor 238 to obtain decoded data and controlinformation sent by the UE 120 a. The receive processor 238 may providethe decoded data to a data sink 239 and the decoded control informationto the controller/processor 240.

The memories 242 and 282 may store data and program codes for BS 110 aand UE 120 a, respectively. A scheduler 244 may schedule UEs for datatransmission on the downlink and/or uplink.

Antennas 252, processors 266, 264, and/or controller/processor 280 ofthe UE 120 a and/or antennas 234, processors 220, 230, and/orcontroller/processor 240 of the BS 110 a may be used to perform thevarious techniques and methods described herein. As shown in FIG. 2 ,the controller/processor 280 of the UE 120 a has an RF exposure manager281 that provides RF exposure continuity (e.g., after an exceptionevent), according to aspects described herein. The RF exposure manager281 may be an example of the RF exposure manager 122 (FIG. 1 ). Althoughshown at the controller/processor, other components of the UE 120 a andBS 110 a may be used to perform the operations described herein. In someembodiments, the BS 110 a (for example, the controller/processor 240)includes an exposure manager configured to provide RF exposurecontinuity for the BS 110 a.

NR may utilize orthogonal frequency division multiplexing (OFDM) with acyclic prefix (CP) on the uplink and downlink. NR may supporthalf-duplex operation using time division duplexing (TDD). OFDM andsingle-carrier frequency division multiplexing (SC-FDM) partition thesystem bandwidth into multiple orthogonal subcarriers, which are alsocommonly referred to as tones, bins, etc. Each subcarrier may bemodulated with data. Modulation symbols may be sent in the frequencydomain with OFDM and in the time domain with SC-FDM. The spacing betweenadjacent subcarriers may be fixed, and the total number of subcarriersmay be dependent on the system bandwidth. The system bandwidth may alsobe partitioned into subbands. For example, a subband may cover multipleresource blocks (RBs).

While the UE 120 a is described with respect to FIGS. 1 and 2 ascommunicating with a BS and/or within a network, the UE 120 a may beconfigured to communicate directly with/transmit directly to another UE120, or with/to another wireless device without relaying communicationsthrough a network. In some embodiments, the BS 110 a illustrated in FIG.2 and described above is an example of another UE 120.

Example RF Transceiver

FIG. 3 is a block diagram of an example RF transceiver circuit 300, inaccordance with certain aspects of the present disclosure. In someembodiments, the RF transceiver circuit 300 is an example of transceiver232 and/or 254, or a portion thereof. The RF transceiver circuit 300includes at least one transmit (TX) path 302 (also known as a transmitchain) for transmitting signals via one or more antennas 306 (which maybe an example of the antennas 234 and/or 252) and at least one receive(RX) path 304 (also known as a receive chain) for receiving signals viathe antennas 306. When the TX path 302 and the RX path 304 share anantenna 306, the paths may be connected with the antenna via aninterface 308, which may include any of various suitable RF devices,such as a switch, a duplexer, a diplexer, a multiplexer, and the like.

Receiving in-phase (I) or quadrature (Q) baseband analog signals from adigital-to-analog converter (DAC) 310, the TX path 302 may include abaseband filter (BBF) 312, a mixer 314, a driver amplifier (DA) 316, anda power amplifier (PA) 318. The BBF 312, the mixer 314, and the DA 316may be included in one or more radio frequency integrated circuits(RFICs). In some embodiments, a mixer (e.g., 314), the DA 316, and/orthe PA 318 may be included in an RFIC.

The BBF 312 filters the baseband signals received from the DAC 310, andthe mixer 314 mixes the filtered baseband signals with a transmit localoscillator (LO) signal to convert the baseband signal of interest to adifferent frequency (e.g., upconvert from baseband to a radiofrequency). This frequency conversion process produces the sum anddifference frequencies between the LO frequency and the frequencies ofthe baseband signal of interest. The sum and difference frequencies arereferred to as the beat frequencies. The beat frequencies are typicallyin the RF range, such that the signals output by the mixer 314 aretypically RF signals, which may be amplified by the DA 316 and/or by thePA 318 before transmission by the antenna 306. While one mixer 314 isillustrated, several mixers may be used to upconvert the filteredbaseband signals to one or more intermediate frequencies (IF) and tothereafter upconvert the intermediate frequency signals to a frequencyfor transmission. Further, while examples discussed herein utilize I andQ signals, those of skill in the art will understand that elements ofthe RF transceiver circuit 300 may be configured to utilize polarmodulation

The RX path 304 may include a low noise amplifier (LNA) 324, a mixer326, and a baseband filter (BBF) 328. The LNA 324, the mixer 326, andoptionally the BBF 328 may be included in one or more RFICs, which mayor may not be the same RFIC(s) that include the TX path components. RFsignals received via the antenna 306 may be amplified by the LNA 324,and the mixer 326 mixes the amplified RF signals with a receive localoscillator (LO) signal to convert the RF signal of interest to adifferent baseband frequency (e.g., downconvert). The baseband signalsoutput by the mixer 326 may be filtered by the BBF 328 before beingconverted by an analog-to-digital converter (ADC) 330 to digital I or Qsignals for digital signal processing. While one mixer 326 isillustrated, several mixers may be used to downconvert the amplified RFsignals to one or more intermediate frequencies and to thereafterdownconvert the intermediate frequency signals to baseband.

Certain transceivers may employ frequency synthesizers with avoltage-controlled oscillator (VCO) to generate a stable, tunable LOsignal with a particular tuning range. Thus, the transmit LO signal maybe produced by a TX frequency synthesizer 320, which may be buffered oramplified by amplifier 322 before being mixed with the baseband (or IF)signals in the mixer 314. Similarly, the receive LO signal may beproduced by an RX frequency synthesizer 332, which may be buffered oramplified by amplifier 334 before being mixed with the RF (or IF)signals in the mixer 326.

A controller 336 may direct the operation of the RF transceiver circuit300, such as transmitting signals via the TX path 302 and/or receivingsignals via the RX path 304. The controller 336 may be a general-purposeprocessor, a digital signal processor (DSP), an application specificintegrated circuit (ASIC), a field programmable gate array (FPGA) orother programmable logic device (PLD), discrete gate or transistorlogic, discrete hardware components, or any combination thereof. Thecontroller 336 may be an example of the controller/processor 240 or 280,or a portion thereof, or may be implemented separate from thecontroller/processor 240, 280. The memory 338 may store data and programcodes for operating the RF transceiver circuit 300. The memory 338 maybe an example of the memory 242 or 282, or a portion thereof, or may beimplemented separate from the memory 242, 282. The controller 336 and/ormemory 338 may include control logic. In certain cases, the controller336 may determine time-averaged RF exposure measurements based ontransmission power levels set by the TX path 302 (e.g., certain levelsof gain at the PA 318) to set a transmission power level for a time slotthat complies with an RF exposure limit set by domestic andinternational regulations as further described herein.

Example RF Exposure Measurement

RF exposure may be expressed in terms of a specific absorption rate(SAR), which measures energy absorption by human tissue per unit massand may have units of watts per kilogram (W/kg). RF exposure may also beexpressed in terms of power density (PD), which measures energyabsorption per unit area and may have units of mW/cm². In certain cases,a maximum permissible exposure (MPE) limit in terms of PD may be imposedfor wireless communication devices using transmission frequencies above6 GHz. The MPE limit is a regulatory metric for exposure based on area,e.g., an energy density limit defined as a number, X, watts per squaremeter (W/m²) averaged over a defined area and time-averaged over afrequency-dependent time window in order to prevent a human exposurehazard represented by a tissue temperature change.

SAR may be used to assess RF exposure for transmission frequencies lessthan 6 GHz, which cover wireless communication technologies such as2G/3G (e.g., CDMA), 4G (e.g., LTE), 5G (e.g., NR in 6 GHz bands), IEEE802.11ac, etc. PD may be used to assess RF exposure for transmissionfrequencies higher than 10 GHz, which cover wireless communicationtechnologies such as IEEE 802.11ad, 802.11ay, 5G in mmWave bands, etc.Thus, different metrics may be used to assess RF exposure for differentwireless communication technologies.

A wireless communication device (e.g., UE 120) may simultaneouslytransmit signals using multiple wireless communication technologies. Forexample, the wireless communication device may simultaneously transmitsignals using a first wireless communication technology operating at orbelow 6 GHz (e.g., 3G, 4G, 5G, etc.) and a second wireless communicationtechnology operating above 6 GHz (e.g., mmWave 5G in 24 to 60 GHz bands,IEEE 802.11ad or 802.11ay). In certain aspects, the wirelesscommunication device may simultaneously transmit signals using the firstwireless communication technology (e.g., 3G, 4G, 5G in sub-6 GHz bands,IEEE 802.11ac, etc.) in which RF exposure is measured in terms of SAR,and the second wireless communication technology (e.g., 5G in 24 to 60GHz bands, IEEE 802.11ad, 802.11ay, etc.) in which RF exposure ismeasured in terms of PD.

To assess RF exposure from transmissions using the first technology(e.g., 3G, 4G, 5G in sub-6 GHz bands, IEEE 802.11ac, etc.), the wirelesscommunication device may include multiple SAR distributions for thefirst technology stored in memory (e.g., memory 242, 282 of FIG. 2 ormemory 338 of FIG. 3 ). Each of the SAR distributions may correspond toa respective one of multiple transmit scenarios supported by thewireless communication device for the first technology. The transmitscenarios may correspond to various combinations of antennas (e.g.,antennas 234 a through 234 t, 252 a through 252 r of FIG. 2 or antenna306 of FIG. 3 ), frequency bands, channels and/or body positions, asdiscussed further below.

The SAR distribution (also referred to as a SAR map) for each transmitscenario may be generated based on measurements (e.g., E-fieldmeasurements) performed in a test laboratory using a model of a humanbody. After the SAR distributions are generated, the SAR distributionsare stored in the memory to enable a processor (e.g., processor 240, 280of FIG. 2 or controller 336 of FIG. 3 ) to assess RF exposure in realtime, as discussed further below. Each SAR distribution includes a setof SAR values, where each SAR value may correspond to a differentlocation (e.g., on the model of the human body). Each SAR value maycomprise a SAR value averaged over a mass, for example 1 g or 10 g, atthe respective location.

The SAR values in each SAR distribution correspond to a particulartransmission power level (e.g., the transmission power level at whichthe SAR values were measured in the test laboratory). Since SAR scaleswith transmission power level, the processor may scale a SARdistribution for any transmission power level by multiplying each SARvalue in the SAR distribution by the following transmission powerscaler:

$\begin{matrix}\frac{Tx_{c}}{Tx_{SAR}} & (1)\end{matrix}$where Tx_(c) is a current transmission power level for the respectivetransmit scenario, and Tx_(SAR) is the transmission power levelcorresponding to the SAR values in the stored SAR distribution (e.g.,the transmission power level at which the SAR values were measured inthe test laboratory).

As discussed above, the wireless communication device may supportmultiple transmit scenarios for the first technology. In certainaspects, the transmit scenarios may be specified by a set of parameters.The set of parameters may include one or more of the following: anantenna parameter indicating one or more antennas used for transmission(i.e., active antennas), a frequency band parameter indicating one ormore frequency bands used for transmission (i.e., active frequencybands), a channel parameter indicating one or more channels used fortransmission (i.e., active channels), a body position parameterindicating the location of the wireless communication device relative tothe user's body location (head, trunk, away from the body, etc.), aparameter indicating whether a device cover and/or type of device coveris positioned on the device, and/or other parameters. In cases where thewireless communication device supports a large number of transmitscenarios, it may be very time-consuming and expensive to performmeasurements for each transmit scenario in a test setting (e.g., testlaboratory). To reduce test time, measurements may be performed for asubset of the transmit scenarios to generate SAR distributions for thesubset of transmit scenarios. In this example, the SAR distribution foreach of the remaining transmit scenarios may be generated by combiningtwo or more of the SAR distributions for the subset of transmitscenarios, as discussed further below.

For example, SAR measurements may be performed for each one of theantennas to generate a SAR distribution for each one of the antennas. Inthis example, a SAR distribution for a transmit scenario in which two ormore of the antennas are active may be generated by combining the SARdistributions for the two or more active antennas.

In another example, SAR measurements may be performed for each one ofmultiple frequency bands to generate a SAR distribution for each one ofthe multiple frequency bands. In this example, a SAR distribution for atransmit scenario in which two or more frequency bands are active may begenerated by combining the SAR distributions for the two or more activefrequency bands.

In certain aspects, a SAR distribution may be normalized with respect toa SAR limit by dividing each SAR value in the SAR distribution by theSAR limit. In this case, a normalized SAR value exceeds the SAR limitwhen the normalized SAR value is greater than one, and is below the SARlimit when the normalized SAR value is less than one. In these aspects,each of the SAR distributions stored in the memory may be normalizedwith respect to a SAR limit.

In certain aspects, the normalized SAR distribution for a transmitscenario may be generated by combining two or more normalized SARdistributions. For example, a normalized SAR distribution for a transmitscenario in which two or more antennas are active may be generated bycombining the normalized SAR distributions for the two or more activeantennas. For the case in which different transmission power levels areused for the active antennas, the normalized SAR distribution for eachactive antenna may be scaled by the respective transmission power levelbefore combining the normalized SAR distributions for the activeantennas. The normalized SAR distribution for simultaneous transmissionfrom multiple active antennas may be given by the following:

$\begin{matrix}{{SAR_{{norm}\_{combined}}} = {\sum\limits_{i = 1}^{i = K}{\frac{{Tx}_{i}}{{Tx}_{SARi}} \cdot \frac{{SAR}_{i}}{{SAR}_{\lim}}}}} & (2)\end{matrix}$where SAR_(lim) is a SAR limit, SAR_(norm_combined) is the combinednormalized SAR distribution for simultaneous transmission from theactive antennas, i is an index for the active antennas, SAR_(i) is theSAR distribution for the i^(th) active antenna, Tx_(i) is thetransmission power level for the i^(th) active antenna, Tx_(SARi) is thetransmission power level for the SAR distribution for the i^(th) activeantenna, and K is the number of the active antennas.

Equation (2) may be rewritten as follows:

$\begin{matrix}{{SAR}_{{norm}\_{combined}} = {\sum\limits_{i = 1}^{i = K}{\frac{{Tx}_{i}}{{Tx}_{SARi}} \cdot {SAR}_{{norm}\_ i}}}} & \left( {3a} \right)\end{matrix}$where SAR_(norm_i) is the normalized SAR distribution for the i^(th)active antenna. In the case of simultaneous transmissions using multipleactive antennas at the same transmitting frequency (e.g., multiple inmultiple out (MIMO)), the combined normalized SAR distribution isobtained by summing the square root of the individual normalized SARdistributions and computing the square of the sum, as given by thefollowing:

$\begin{matrix}{{SAR}_{{norm}\_{combined}\_{MIMO}} = {\left\lbrack {\sum\limits_{i = 1}^{i = K}\sqrt{\frac{{Tx}_{i}}{{Tx}_{SARi}} \cdot {SAR}_{{norm}\_ i}}} \right\rbrack^{2}.}} & \left( {3b} \right)\end{matrix}$

In another example, normalized SAR distributions for different frequencybands may be stored in the memory. In this example, a normalized SARdistribution for a transmit scenario in which two or more frequencybands are active may be generated by combining the normalized SARdistributions for the two or more active frequency bands. For the casewhere the transmission power levels are different for the activefrequency bands, the normalized SAR distribution for each of the activefrequency bands may be scaled by the respective transmission power levelbefore combining the normalized SAR distributions for the activefrequency bands. In this example, the combined SAR distribution may alsobe computed using Equation (3a) in which i is an index for the activefrequency bands, SAR_(norm_i) is the normalized SAR distribution for thei^(th) active frequency band, Tx_(i) is the transmission power level forthe i^(th) active frequency band, and Tx_(SARi) is the transmissionpower level for the normalized SAR distribution for the i^(th) activefrequency band.

To assess RF exposure from transmissions using the second technology(e.g., 5G in 24 to 60 GHz bands, IEEE 802.11ad, 802.11ay, etc.), thewireless communication device may include multiple PD distributions forthe second technology stored in the memory (e.g., memory 242, 282 ofFIG. 2 or memory 338 of FIG. 3 ). Each of the PD distributions maycorrespond to a respective one of multiple transmit scenarios supportedby the wireless communication device for the second technology. Thetransmit scenarios may correspond to various combinations of antennas(e.g., antennas 234 a through 234 t, 252 a through 252 r of FIG. 2 orantenna 306 of FIG. 3 ), frequency bands, channels and/or bodypositions, as discussed further below.

The PD distribution (also referred to as PD map) for each transmitscenario may be generated based on measurements (e.g., E-fieldmeasurements) performed in a test laboratory using a model of a humanbody. After the PD distributions are generated, the PD distributions arestored in the memory to enable the processor (e.g., processor 240, 280of FIG. 2 or controller 336 of FIG. 3 ) to assess RF exposure in realtime, as discussed further below. Each PD distribution includes a set ofPD values, where each PD value may correspond to a different location(e.g., on the model of the human body).

The PD values in each PD distribution correspond to a particulartransmission power level (e.g., the transmission power level at whichthe PD values were measured in the test laboratory). Since PD scaleswith transmission power level, the processor may scale a PD distributionfor any transmission power level by multiplying each PD value in the PDdistribution by the following transmission power scaler:

$\begin{matrix}\frac{{Tx}_{c}}{{Tx}_{PD}} & (4)\end{matrix}$where Tx_(c) is a current transmission power level for the respectivetransmit scenario, and TX_(PD) is the transmission power levelcorresponding to the PD values in the PD distribution (e.g., thetransmission power level at which the PD values were measured in thetest laboratory).

As discussed above, the wireless communication device may supportmultiple transmit scenarios for the second technology. In certainaspects, the transmit scenarios may be specified by a set of parameters.The set of parameters may include one or more of the following: anantenna parameter indicating one or more antennas used for transmission(i.e., active antennas), a frequency band parameter indicating one ormore frequency bands used for transmission (i.e., active frequencybands), a channel parameter indicating one or more channels used fortransmission (i.e., active channels), a body position parameterindicating the location of the wireless communication device relative tothe user's body location (head, trunk, away from the body, etc.), aparameter indicating whether a device cover and/or type of device coveris positioned on the device, and/or other parameters. In cases where thewireless communication device supports a large number of transmitscenarios, it may be very time-consuming and expensive to performmeasurements for each transmit scenario in a test setting (e.g., testlaboratory). To reduce test time, measurements may be performed for asubset of the transmit scenarios to generate PD distributions for thesubset of transmit scenarios. In this example, the PD distribution foreach of the remaining transmit scenarios may be generated by combiningtwo or more of the PD distributions for the subset of transmitscenarios, as discussed further below.

For example, PD measurements may be performed for each one of theantennas to generate a PD distribution for each one of the antennas. Inthis example, a PD distribution for a transmit scenario in which two ormore of the antennas are active may be generated by combining the PDdistributions for the two or more active antennas.

In another example, PD measurements may be performed for each one ofmultiple frequency bands to generate a PD distribution for each one ofthe multiple frequency bands. In this example, a PD distribution for atransmit scenario in which two or more frequency bands are active may begenerated by combining the PD distributions for the two or more activefrequency bands.

In certain aspects, a PD distribution may be normalized with respect toa PD limit by dividing each PD value in the PD distribution by the PDlimit. In this case, a normalized PD value exceeds the PD limit when thenormalized PD value is greater than one, and is below the PD limit whenthe normalized PD value is less than one. In these aspects, each of thePD distributions stored in the memory may be normalized with respect toa PD limit.

In certain aspects, the normalized PD distribution for a transmitscenario may be generated by combining two or more normalized PDdistributions. For example, a normalized PD distribution for a transmitscenario in which two or more antennas are active may be generated bycombining the normalized PD distributions for the two or more activeantennas. For the case in which different transmission power levels areused for the active antennas, the normalized PD distribution for eachactive antenna may be scaled by the respective transmission power levelbefore combining the normalized PD distributions for the activeantennas. The normalized PD distribution for simultaneous transmissionfrom multiple active antennas may be given by the following:

$\begin{matrix}{{PD}_{{norm}\_{combined}} = {\sum\limits_{i = 1}^{i = L}{\frac{{Tx}_{i}}{{Tx}_{PDi}} \cdot \frac{{PD}_{i}}{{PD}_{\lim}}}}} & (5)\end{matrix}$where PD_(lim) is a PD limit, PD_(norm_combined) is the combinednormalized PD distribution for simultaneous transmission from the activeantennas, i is an index for the active antennas, PD_(i) is the PDdistribution for the i^(th) active antenna, Tx_(i) is the transmissionpower level for the i^(th) active antenna, TX_(PDi) is the transmissionpower level for the PD distribution for the i^(th) active antenna, and Lis the number of the active antennas.

Equation (5) may be rewritten as follows:

$\begin{matrix}{{PD}_{{norm}\_{combined}} = {\sum\limits_{i = 1}^{i = L}{\frac{{Tx}_{i}}{{Tx}_{PDi}} \cdot {PD}_{{norm}\_ i}}}} & \left( {6a} \right)\end{matrix}$where PD_(norm_i) is the normalized PD distribution for the i^(th)active antenna. In the case of simultaneous transmissions using multipleactive antennas at the same transmitting frequency (e.g., MIMO), thecombined normalized PD distribution is obtained by summing the squareroot of the individual normalized PD distributions and computing thesquare of the sum, as given by the following:

$\begin{matrix}{{PD}_{{norm}\_{combined}\_{MIMO}} = {\left\lbrack {\sum\limits_{i = 1}^{i = L}\sqrt{\frac{{Tx}_{i}}{{Tx}_{PDi}} \cdot {PD}_{{norm}\_ i}}} \right\rbrack^{2}.}} & \left( {6b} \right)\end{matrix}$

In another example, normalized PD distributions for different frequencybands may be stored in the memory. In this example, a normalized PDdistribution for a transmit scenario in which two or more frequencybands are active may be generated by combining the normalized PDdistributions for the two or more active frequency bands. For the casewhere the transmission power levels are different for the activefrequency bands, the normalized PD distribution for each of the activefrequency bands may be scaled by the respective transmission power levelbefore combining the normalized PD distributions for the activefrequency bands. In this example, the combined PD distribution may alsobe computed using Equation (6a) in which i is an index for the activefrequency bands, PD_(norm_i) is the normalized PD distribution for thei^(th) active frequency band, Tx_(i) is the transmission power level forthe i^(th) active frequency band, and TX_(PDi) is the transmission powerlevel for the normalized PD distribution for the i^(th) active frequencyband.

As discussed above, the UE 120 may simultaneously transmit signals usingthe first technology (e.g., 3G, 4G, IEEE 802.11ac, etc.) and the secondtechnology (e.g., 5G, IEEE 802.11ad, etc.), in which RF exposure ismeasured using different metrics for the first technology and the secondtechnology (e.g., SAR for the first technology and PD for the secondtechnology). In this case, the processor 280 may determine a firstmaximum allowable power level for the first technology and a secondmaximum allowable power level for the second technology fortransmissions in a time slot that comply with RF exposure limits. Duringthe time slot, the transmission power levels for the first and secondtechnologies are constrained (i.e., bounded) by the determined first andsecond maximum allowable power levels, respectively, to ensurecompliance with RF exposure limits, as further below. In the presentdisclosure, the term “maximum allowable power level” refers to a“maximum allowable power level” imposed by an RF exposure limit unlessstated otherwise. It is to be appreciated that the “maximum allowablepower level” is not necessarily equal to the absolute maximum powerlevel that complies with an RF exposure limit and may be less than theabsolute maximum power level that complies with the RF exposure limit(e.g., to provide a safety margin). The “maximum allowable power level”may be used to set a power level limit on a transmission at atransmitter such that the power level of the transmission is not allowedto exceed the “maximum allowable power level” to ensure RF exposurecompliance.

The processor (e.g., 240, 280, 336) may determine the first and secondmaximum allowable power levels as follows. The processor may determine anormalized SAR distribution for the first technology at a firsttransmission power level, determine a normalized PD distribution for thesecond technology at a second transmission power level, and combine thenormalized SAR distribution and the normalized PD distribution togenerate a combined normalized RF exposure distribution (referred tosimply as a combined normalized distribution below). The value at eachlocation in the combined normalized distribution may be determined bycombining the normalized SAR value at the location with the normalizedPD value at the location or another technique.

The processor may then determine whether the first and secondtransmission power levels comply with RF exposure limits by comparingthe peak value in the combined normalized distribution with one. If thepeak value is equal to or less than one (i.e., satisfies thecondition≤1), then the processor 280 may determine that the first andsecond transmission power levels comply with RF exposure limits (e.g.,SAR limit and PD limit) and use the first and second transmission powerlevels as the first and second maximum allowable power levels,respectively, during the time slot. If the peak value is greater thanone, then the processor may determine that the first and secondtransmission power levels do not comply with RF exposure limits. Thecondition for RF exposure compliance for simultaneous transmissionsusing the first and second technologies may be given by:SAR_(norm)+PD_(norm)≤1  (7).

The normalized SAR distribution in equation (7) may be generated bycombining two or more normalized SAR distributions as discussed above(e.g., for a transmit scenario using multiple active antennas).Similarly, the normalized PD distribution in equation (7) may begenerated by combining two or more normalized PD distributions asdiscussed above (e.g., for a transmit scenario using multiple activeantennas). In this case, the condition for RF exposure compliance inequation (7) may be rewritten using equations (3a) and (6a) as follows:

$\begin{matrix}{{{\sum\limits_{i = 1}^{i = K}{\frac{{Tx}_{i}}{{Tx}_{SARi}} \cdot {SAR}_{{norm}\_ i}}} + {\sum\limits_{i = 1}^{i = L}{\frac{{Tx}_{i}}{{Tx}_{PDi}} \cdot {PD}_{{norm}\_ i}}}} \leq 1.} & (8)\end{matrix}$For the MIMO case, equations (3b) and (6b) may be combined instead. Asshown in equation (8), the combined normalized distribution may be afunction of transmission power levels for the first technology andtransmission power levels for the second technology. All the points inthe combined normalized distribution may meet the normalized limit ofone in equation (8). Additionally, when combining SAR and PDdistributions, the SAR and PD distributions may be aligned spatially oraligned with their peak locations so that the combined distributiongiven by equation (8) represents combined RF exposure for a givenposition of a human body.

Example Exception Robust Time Averaged RF Exposure Compliance Continuity

Time-averaged RF exposure compliance (e.g., SAR or MPE/PD) may providedesirable device performance, as well as ensure user safety at thedevice. In certain cases (such as normal runtime operations), the device(e.g., a UE) has an active system that ensures RF exposure compliance atall times, based upon varying time windows of power history. When the UEoperation is halted by an exception condition (such as an assert, crash,or reset), and then the UE subsequently returns to normal runtimeoperations, the UE may lose all of the recent RF exposure history usedto ensure time-averaged RF exposure compliance. For shorter RF exposuretime windows (e.g., 4 seconds for NR Frequency Range (FR) 2), resettingthe RF exposure history may be acceptable, since the time that the UEtakes to reboot and begin a normal transmit operation may be longer thanthe time window over which power history is to be averaged. For certaintransmission frequencies (e.g., NR FR1 and legacy 2/3/4G wireless widearea network (WWAN)), and depending upon the regulatory standard used,though, the time window can be longer (e.g., up to 360 seconds). Due tothe longer time window for determining RF exposure compliance forcertain transmission frequencies, the UE may start afresh with notransmit power history. As such, the lack of transmit power history maydisrupt operation of the software/components ensuring RF exposurecompliance. For example, in the absence of proper procedures the UE maytransmit data using a transmit power that exceeds an RF exposure limitfor the time window due to the lack of a transmit power history beforethe exception condition in the time window.

Aspects of the present disclosure provide various techniques forproviding continuity of RF exposure information following variousexception events (such as an error, reset, crash, or reboot affectingthe operations of the UE or in particular a modem of the UE, and/or anevent which results in a portion of time during which RF exposure isunknown or indeterminate). In certain aspects, the UE may periodicallystore RF exposure information (such as transmit power and/ortime-averaged RF exposure measurements of the transmit power history) inmemory resistant to corruption from an exception event. When anexception event occurs (such as the UE rebooting or the UE's modemresetting, or an event which causes the UE to experience or detect anamount of time during which RF exposure information is unknown orindeterminate), the UE may use the stored RF exposure information todetermine a transmit power in compliance with the RF exposure limit. Thetechniques for providing RF exposure continuity described herein mayenable the UE to remain in compliance with the RF exposure limits afterthe UE encounters an exception event and/or may allow the UE to transmitat a higher power in certain such circumstances while maintaining safetyfor the user after an exception event. The techniques for providing RFexposure continuity described herein may provide a low-power solutionthat consumes an acceptable amount of power to store the RF exposuremeasurements without significantly affecting the battery life of the UE.In certain cases, the techniques for providing RF exposure continuitydescribed herein may facilitate desirable power consumption, forexample, due to relatively high transmit powers (e.g., exceeding the RFexposure limit) used before the exception event when taking into accountthe stored RF exposure information. In certain cases, the techniques forproviding RF exposure continuity described herein may enable desirabletransmit powers, for example, due to relatively low transmit powers(e.g., less than the RF exposure limit) used before the exception eventwhen taking into account the stored RF exposure information.

Certain aspects of the present disclosure involve using a UE's onboardpower management integrated circuit (PMIC), which may include a counter.In certain cases, the counter may be based on a real-time clock (RTC).The RTC may monotonically count upward, even when the UE resets or poweris momentarily lost. The RTC may allow the UE software to periodicallytake a snapshot of the transmit power history using the PMIC RTCtimestamp, and save the transmit power history in internal static memorythat is resistant to corruption due to an exception event. Upon orshortly after a reset, the UE software may check the memory location ininternal static memory for an RTC timestamp, optionally aconsistency/reliability indicator (e.g., a checksum, such as a cyclicredundancy check (CRC)), and data (e.g., a CRC-protected set of data)indicating the recent transmit power history. If the CRC passes, forexample, the current (post-reset) RTC timestamp is used to determine howold the transmit power history is, and the UE's compliance algorithmtransmit power history bookkeeping is updated accordingly. Thetechniques for providing RF exposure continuity described herein mayensure compliance at all times, even across unexpected resets or otherexception events (e.g., if recent records of exposure are lost orunknown for any reason). If the CRC passes, but the timestamp is oldenough to not fall within the longest time-averaging window, thetransmit power history may not be used. If the CRC fails, the UE mayenter a failsafe mode where the transmit power is restricted for theinitial duration of the longest window, ensuring compliance at a cost ofinitial performance.

FIG. 4 is a flow diagram illustrating example operations 400 forwireless communication, in accordance with certain aspects of thepresent disclosure. The operations 400 may be performed, for example, bya UE (e.g., the UE 120 a in the wireless communication network 100), BS,or Customer Premises Equipment (CPE). The operations 400 may beimplemented as software components that are executed and run on one ormore processors (e.g., controller/processor 240, 280 of FIG. 2 ,controller 336 of FIG. 3 ). Further, the transmission of signals by theUE (or BS, CPE) in the operations 400 may be enabled, for example, byone or more antennas (e.g., antennas 234, 252 of FIG. 2 , antenna 306 ofFIG. 3 ). In certain aspects, the transmission and/or reception ofsignals by the UE may be implemented via a bus interface of one or moreprocessors (e.g., controller/processor 240, 280, controller 336 of FIG.3 ) obtaining and/or outputting signals.

The operations 400 may begin, at block 402, where the UE may transmit afirst signal at a first transmission power based on time-averaged RFexposure measurements over a time window. At block 404, the UE may storeRF exposure information associated with the time window. At block 406,the UE may detect that an exception event associated with the UEoccurred. At block 408, the UE may transmit a second signal at a secondtransmission power based at least in part on the stored RF exposureinformation in response to the detection of the event.

In aspects, the UE (for example using components described in FIGS. 2and/or 3 , and potentially in combination with the RF exposure manager122, 281) may be communicating with a base station, such as the BS 110.For example, at block 402 and/or block 408, the UE may be transmitting,to the base station, user data on a physical uplink shared channel(PUSCH) or various uplink feedback (e.g., uplink control information orhybrid automatic repeat request (HARQ) feedback) on a physical uplinkcontrol channel (PUCCH). In certain cases, the UE may be communicatingwith another UE. For example, at block 402 and/or block 408, the UE maybe transmitting, to the other UE, user data and/or various feedback onsidelink channels.

In aspects, the RF exposure information may include a history oftransmission powers and/or time-averaged RF exposure measurements. Incertain cases, the RF exposure information may include a sum of thetime-averaged RF exposure measurements, a sum of the transmission powerswithin the time window at a time corresponding to a timestamp, or anintegration of transmit powers over time. In certain cases, the RFexposure information may include separate values for each of thetime-averaged RF exposure measurements or the transmission powers withinthe time window at the time corresponding to the timestamp.

At block 404, the UE (e.g., the RF exposure manager 122, 281) mayperiodically store the RF exposure information. That is, the UE maystore the RF exposure information according to a period, such as every50 milliseconds (ms), 500 ms, or 1 second (s). In other words, the UEmay store the RF exposure information at periodic intervals, forexample, of 50 ms, 500 ms or 1 s.

At block 404, the UE may store the RF exposure information in a memoryresistant to corruption from the exception event. That is, the memorymay be configured to store data (such as the RF exposure information)before or as the exception event occurs, where the exception event doesnot corrupt the stored data. In certain cases, the UE may store the RFexposure information as the exception event occurs, for example, whenthe UE may still be transmitting during the exception event. Forexample, the memory may be non-volatile memory or static memory separatefrom memory used for a file system, as further described herein withrespect to FIG. 6 . In certain cases, the memory used for the filesystem may consume too much power to provide a low-power memory solutionfor storing the RF exposure information. In certain aspects, however,the RF exposure information may be stored in the memory used for thefile system.

At block 404, the UE may store the RF exposure information with atimestamp. The timestamp may correspond to a time (e.g., an absolute orrelative time) when a most recent time-averaged RF exposure measurementis generated or when the (most) recent transmission is sent by the UE.In other words, the RF exposure information may include the (most)recent time-averaged RF exposure measurement or the (most) recenttransmit power history.

In aspects, the timestamp associated with the RF exposure informationmay be used to determine whether to use the RF exposure information indetermining the second transmission power for the second signal. Forexample, at block 408, the UE may transmit the second signal at thesecond transmission power based at least in part on the stored RFexposure information if the timestamp of the RF exposure information iswithin a current time window (e.g., in response to determining that thetimestamp of the RF exposure information is within a current timewindow), where the current time window may look backwards in timestarting at a current timestamp, for example, corresponding to when theUE recovers from the exception event. In other words, if the timestampof the RF exposure information is outside the current time window, theUE may not consider the RF exposure information in determining thesecond transmission power for the second signal. In certain cases, theUE may determine a time delta between the timestamp of the RF exposureinformation and a current timestamp (for example, corresponding to whenthe UE recovers from the exception event), and if the time delta isgreater than (or equal to) the duration of the (current or longest) timewindow, the UE may not consider the RF exposure information indetermining the second transmission power for the second signal.Otherwise, if the time delta is less than (or equal to) the duration ofthe (current or longest) time window, the UE may use the RF exposureinformation in determining the second transmission power for the secondsignal. As described above, the time window may vary based on frequencyand/or regulation/standard; thus, a certain time delta may correspond tothe UE using the RF exposure information in determining the secondtransmission power for the second signal in certain scenarios (e.g.,transmission frequency, geographic location, etc.) and may correspond tothe UE ignoring the RF exposure information in other scenarios.

In certain aspects, storing the RF exposure information may involveobtaining the timestamp from a counter or a clock. For example, the UEmay obtain the timestamp from a counter resistant to corruption by theexception event. The counter may be resistant to the exception event bybeing able to continue providing timestamps independent of the exceptionevent. That is, the counter may continue to the count monotonicallyupward during the exception event without losing any increments in time.In certain cases, the counter may be based on a real-time clock.

As an example, suppose the UE reboots, and when the UE returns to normaloperations, the UE checks whether the timestamp of the stored RFexposure information is within the current (or longest) time window. Forexample, the UE may obtain a current timestamp from the counter andcompare the current timestamp with the timestamp of the RF exposureinformation. If the timestamp of the stored RF exposure information iswithin the current time window, the UE may use the stored RF exposureinformation in determining the second transmission power for the secondsignal. The UE may continue to use the RF exposure information tosupplement RF exposure measurements until the timestamp is outside ofthe current time window. If the timestamp of the RF exposure informationis outside the current time window (i.e., too much time has passed sincethe exception event), the UE may not use the stored RF exposureinformation in determining the second transmission power of the secondsignal.

In certain cases, the RF exposure information and/or timestamp may bestored with a check value or other reliability or fidelity indicatorused to detect data inconsistencies, such as a cyclic redundancy check(CRC) or checksum. In certain cases, the check value may include aremainder in a CRC of the RF exposure information and/or timestamp.

In certain aspects, determining whether to use the RF exposureinformation may depend on the check value passing a CRC or confirmingthe fidelity of the RF exposure information based on the reliabilityindicator. For example, the UE may transmit the second signal at thesecond transmission power based on supplementing time-averaged RFexposure measurements over the current time window with the stored RFexposure information if the CRC of the RF exposure information matchesthe check value (e.g., in response to determining that the CRC of the RFexposure information matches the check value). In certain aspects, ifthe CRC of the RF exposure information passes, the RF exposureinformation may be used to determine the second transmission power forthe second signal. If the CRC of the RF exposure information fails, theUE may enter a failsafe mode where a lower RF exposure limit than thestandard RF exposure limit may be used to determine the transmissionpower for the second signal. For example, the failsafe mode may includeusing an assumed prior transmission power or exposure (e.g., a maximumtransmission power or exposure over the duration of the earlier/priorpart of the current time window) to determine the transmission power forthe second signal in order to ensure safety for the user and compliancewith any applicable exposure limits. In certain cases, the failsafe modemay be used if the RF exposure information is outside of the currenttime window when returning to normal operations after the exceptionevent. In certain situations in which the transmission power for thesecond signal is based on the stored RF exposure information, however,the stored RF exposure information will indicate that the previoustransmission power or exposure is less than would have been assumed inthe failsafe mode, and thus, the transmission power for the secondsignal may be higher than would have been used in the failsafe modewhile still maintaining safe operating conditions for the user.

In certain cases, the second transmission power at block 408 may bebased on supplementing time-averaged RF exposure measurements with thestored RF exposure information. For example, suppose the time window is100 seconds, such that the stored RF exposure information represents 100seconds of transmission history. If the exception event only took 10seconds, there is still 90 seconds of RF exposure information availableto supplement new RF exposure measurements taken during normaloperations after the exception event.

In certain cases, the second transmission power at block 408 may bebased at least in part on the stored RF exposure information when atleast one RF exposure measurement is missing from the time window. Forexample, the UE may lack RF exposure measurements due to the exceptionevent. That is, the UE may be unable to communicate with other wirelesscommunication devices and transmit signals during the exception event.The UE may lack a transmission power history during the exception event,and as a result, there may be RF exposure measurements missing from thetime window.

In aspects, the UE may detect the exception event (at block 406) throughvarious means. For example, the UE (e.g., the RF exposure manager 122,281) may monitor certain logs, statistics, or an interface state(enabled or disabled) associated with one or more wireless communicationcomponents (such as a modem) of the UE to determine whether the UE hasencountered an exception event. Certain messages (e.g., error messagesor boot messages) in the logs may indicate that an exception event hasoccurred, the various transmit statistics (e.g., transmit packets ortransmit bytes) resetting to zero may indicate an exception eventoccurred, or the modem switching from an enabled state (e.g., the modemis online and operational) to a disabled state (e.g., the modem isoffline) may indicate an exception event occurred. In certain cases, theUE may monitor the modem for a specific interrupt that indicates anexception event has occurred. In some embodiments, the RF exposuremanager is implemented in the modem, and the RF exposure manager mayrecognize that the modem was (temporarily) disabled by checking the logsor transmit statistics referenced above. Thus, software implementedseparate from the modem may monitor the modem and/or operation thereofand perform the determination at block 406, or the modem may monitoritself to perform the determination at block 406. Such checks may beperiodically performed (e.g., on the same order as the storage of the RFexposure information, such as every 50 ms, 500 ms or 1 s, or accordingto another period not related to the storage of the RF exposureinformation), performed based on certain occurrences (e.g., new databeing loaded into a transmit buffer), etc.

In aspects, the exception event may include various events where the UEtemporarily ceases communication or an event which results in a portionof time during which the UE's RF exposure is unknown or indeterminate.For example, the exception event may include the modem shutting down,the modem resetting, the modem rebooting, the modem crashing, or themodem encountering an error. In certain cases, the exception event mayinclude an error, a reset, a crash, or a reboot affecting an operationof the UE or the modem used in transmitting the first and secondsignals. For example, the error, reset, crash, or reboot of the modem oranother component may render the UE temporarily inoperable from awireless communication standpoint or temporarily inoperable fromtracking RF exposure. That is, the error, reset, crash, or reboot mayprevent the UE from communicating wirelessly, such as transmittingsignals from the UE's antenna(s), or from determining the RF exposurefor a duration of time.

In aspects, the second transmission power at block 408 may be based on atype of exception event and/or a confidence in a likelihood oftransmission during the portion of the time window corresponding to themissing RF exposure measurements. For example, if the RF exposuremanager determines that communications (or at least transmissions)ceased during that portion of the time window (e.g., based on themessages, logs, statistics, etc. described above), the RF exposuremanager may allocate zero transmission power to that portion of timewhen calculating the second transmission power. In other embodiments,the RF exposure manager allocates a minimum transmit power (e.g., apower required to maintain a certain link) to the portion of the timewindow corresponding to the missing RF exposure measurements, forexample during conservative operation, when calculating the secondtransmission power. In other aspects, if it cannot be determined why anexception event occurred or that transmission ceased during the portionof the time window corresponding to the missing RF exposuremeasurements, the RF exposure manager may allocate a maximum allowablepower level (or other predetermined transmit power) to that portion oftime to calculate the second transmission power. In some aspects, aconfidence level may be determined (e.g., based on data in a transmitbuffer, transmit logs, communications received from another device,etc.) with respect to whether the device was transmitting during theportion of the time window corresponding to the missing RF exposuremeasurements, and the second transmission power determined basedthereon. For example, comparison of the confidence level to a thresholdmay determine whether a zero or minimum transmission power level isallocated, or whether a maximum allowable power level (or other powerlevel) is allocated to that portion of the time window. In someembodiments, a confidence level may be used to proportionally allocatetransmission power to that portion of the time window.

In aspects, the time-averaged RF exposure measurements (e.g., stored atblock 404) may include at least one of a time-averaged SAR or atime-averaged PD. In aspects, the time window may be in a range from 1second to 360 seconds. For example, the time window may be 100 secondsor 360 seconds. The range from 1 second to 360 seconds is an example,and other suitable values for the time window may be used. In certaincases, the time window may be less than 1 second, such as 500milliseconds. In certain cases, the time window may be greater than 360seconds, such as 600 seconds.

FIG. 5 is a diagram illustrating time-averaged RF exposure over a timewindow T1, in accordance with certain aspects of the present disclosure.The UE may determine the time-averaged RF exposure using time-averagedRF exposure measurements (for example, the various RF measurementscorresponding to intervals (i) through (i−m)) across the time window T1.In certain cases, the UE may determine the RF exposure measurementsbased on a conversion model or scaling factor between SAR/PD and thetransmission powers used at each transmission interval (such asintervals (i) through (i−m)).

In this example, the RF exposure measurements 502 may have been storedas RF exposure information prior to an exception event, for example, asdescribed herein with respect to the operations 400. In aspects, the RFexposure information may have been stored as a sum of the RF exposuremeasurements 502 or as separate values for each of the RF exposuremeasurements 502. Within the time window T1, the UE may have encounteredan exception event. After returning to normal operations or recoveringfrom the exception event, the UE may use the RF exposure information torepresent the RF exposure measurements prior to the exception event indetermining the time-averaged RF exposure if the RF exposure informationis within the time window T1. In this example, the RF exposureinformation is within the time window T1 (for example, the current timewindow may span from i-m to i), and as such, the UE may use the RFexposure information in determining a transmission power in compliancewith the respective RF exposure requirements based on the time-averagedRF exposure. In certain cases, the UE may use a portion of the RFexposure information in determining the time-averaged RF exposure. Forexample, as the UE continues to determine the time-averaged RF exposurefor the rolling time window T1 (for example, the current time window mayadvance (i.e., shift in time) by a time interval to span from i−1 toi+1), the UE may use a portion of the RF exposure information thatcorresponds to the remaining time intervals (e.g., intervals (i−1) and(i−k)) in the time window T1.

If the RF exposure information is outside the time window T1, the UE maynot use the RF exposure information in determining the transmissionpower, and in certain cases, the UE may operate in a failsafe mode, forexample, as described herein with respect to the operations 400. As anexample, suppose a timestamp associated with the RF exposure informationplaced the RF exposure information outside the time window T1 at aninterval (i−n). The UE may determine that the RF exposure information isoutside the time window by comparing the timestamp associated with theRF exposure information with a timestamp associated with the currentinterval (i). As described herein, if the time delta between thetimestamp associated with the RF exposure information and the timestampassociated with the current interval (i) is greater than or equal to theduration of the time window T1, the UE may not use the RF exposureinformation in determining the transmission power.

FIG. 6 is a block diagram illustrating a design of an example wirelesscommunication device 600 (e.g., the UE 120, BS 110) for implementing RFexposure continuity following an exception event, in accordance withcertain aspects of the present disclosure. As shown, the wirelesscommunication device 600 may include a transceiver 602 (which may be anexample of the transceivers 232, 254, 300), one or more antennas 604(which may be an example of the antennas 234, 252, 306), a modem 606, aprocessor 608, a memory 610 (which may be an example of the memory 242,282, 338), and a counter 612. In certain cases, the counter 612 may beintegrated with or included in a PMIC 614. In certain cases, thewireless communication device 600 may also include an applicationprocessor 616 and a file system memory 618. In some embodiments, one orboth of the modem 606 and the processor 608 are implemented by or withincomponents of FIG. 2 such as 212, 220, 230, 236, 238, 239, 240, 244,256, 258, 260, 262, 264, 266, and/or 280, and/or controller 336 of FIG.3 . An RF exposure manager (e.g., 122, 281) may be implemented in themodem 606 and/or processor 608.

The wireless communication device 600 may transmit various signals fromthe transceiver 602 and the one or more antennas 604 coupled to thetransceiver 602. The modem 606 may provide modulated signals to thetransceiver 602 and provide instructions to the transceiver 602 toadjust the transmission power of the signals to comply with various RFexposure limits. For example, the modem 606 may provide, to thetransceiver 602, instructions on the first transmission power and thesecond transmission power as described herein with respect to theoperations 400. The processor 608 may obtain the current RF exposureinformation from the modem 606 and periodically store the RF exposureinformation in the memory 610 with a timestamp (and a CRC), as describedherein with respect to the operations 400. In aspects, the memory 610may be tightly coupled with the modem 606 and/or processor 608 andprovide a lower power solution for repeatedly storing the RF exposureinformation compared to the file system memory 618. In certain aspects,the memory 610 may be resistant to corruption (e.g., electricallyisolated from the modem 606 or certain components of the modem 606) dueto an exception event affecting the operations of the wirelesscommunication device 600 or modem 606. Those of skill in the art willunderstand that the exception event that triggers the use of the storedRF exposure information may be associated with other components thataffect the operability of the wireless communication device 600, such asvarious circuitry, memory, or processors. In certain cases, theprocessor 608 and/or memory 610 may be integrated with the modem 606.

The processor 608 may obtain the timestamp from the counter 612, whichmay be integrated with the PMIC 614, such that the counter 612 maycontinue to keep time when the wireless communication device 600 isshutdown or rebooting, which in turn may trigger an exception eventassociated with the modem 606. For example, the PMIC 614 may provide asource of power for the counter 612 to continue keeping track of thetime while the wireless communication device 600 is shut down (i.e., inan off state), resetting, or rebooting. In certain cases, the counter612 may be based on a real-time clock (RTC), which may be integratedwith the PMIC. When the wireless communication device 600 returns to anormal operating state or at least recovers from the exception event,the processor 608 may obtain the current timestamp from the counter 612and compare the current timestamp with the timestamp stored with the RFexposure information to determine whether the timestamp is within a timewindow associated with an RF exposure limit. If the timestamp of the RFexposure information is within the time window (e.g., T1 of FIG. 5 ),the wireless communication device 500 may use the stored RF exposureinformation to determine a transmit power in compliance with an RFexposure limit.

The application processor 616 may be a processor included with asystem-on-a-chip (SoC). For example, the application processor 616 mayrun an operating system that provides a graphical environment for a userto access various applications (such as a web browser, streamingapplications, social media applications, etc.). The file system memory618 may store the operating system, applications, and various user data.In aspects, the memory 610 may be non-volatile memory separate from thefile system memory 618. In certain cases, the application processor 616and file system memory 618 may store the RF exposure information as analternative to or in addition to the processor 608 and memory 610.Further, in certain cases the counter 612 may be implemented on the SoC.For example, a global counter on the SoC that monotonically increasesmay be used when determining the timestamp. In some such cases, thecounter on the SoC resets when the application processor 616 crashes oris otherwise stopped. In these cases, the RTC in the PMIC 614 mayprovide an advantage because the RTC will continue counting when theapplication processor 616 is disabled (e.g., due to a reboot, shutdown,etc.).

FIG. 7 is a signaling flow illustrating example operations for providingRF exposure continuity following an exception event, in accordance withcertain aspects of the present disclosure. At 702, the UE 120 maytransmit a first signal to the BS 110 at a first transmission powerbased on time-averaged RF exposure measurements over a time window(e.g., the time window T1 of FIG. 5 ). At 704, the UE 120 mayperiodically store RF exposure information associated with the timewindow. At 706, the UE 120 may encounter an exception event associatedwith the UE or a modem (e.g., the modem 606). For example, the UE 120may reboot causing the modem to power cycle. In certain cases, the modemmay crash or encounter an error, for example, due to a software bug oroverheating. At 708, the UE 120 may detect that the exception eventoccurred, for example, as described herein with respect to theoperations 400. At 710, the UE 120 may transmit a second signal at asecond transmission power based at least in part on the stored RFexposure information in response to the detection of the event, forexample, as described herein with respect to the operations 400.

FIG. 8 illustrates a communications device 800 (e.g., the UE 120) thatmay include various components (e.g., corresponding tomeans-plus-function components) configured to perform operations for thetechniques disclosed herein, such as the operations illustrated in FIG.4 . The communications device 800 includes a processing system 802coupled to a transceiver 808 (e.g., a transmitter and/or a receiver).The transceiver 808 is configured to transmit and receive signals forthe communications device 800 via an antenna 810, such as the varioussignals as described herein. The processing system 802 may be configuredto perform processing functions for the communications device 800,including processing signals received and/or to be transmitted by thecommunications device 800.

The processing system 802 includes a processor 804 coupled to acomputer-readable medium/memory 812 via a bus 806. In certain aspects,the computer-readable medium/memory 812 is configured to storeinstructions (e.g., computer-executable code) that when executed by theprocessor 804, cause the processor 804 to perform the operations 400illustrated in FIG. 4 , or other operations for performing the varioustechniques discussed herein for providing RF exposure continuity afteran exception event. In certain aspects, computer-readable medium/memory812 stores code for transmitting 814, code for storing 816, and/or codefor detecting 818. In certain aspects, the processing system 802 hascircuitry 820 configured to implement the code stored in thecomputer-readable medium/memory 812. In certain aspects, the circuitry820 is coupled to the processor 804 and/or the computer-readablemedium/memory 812 via the bus 806. For example, the circuitry 820includes circuitry for transmitting 822, circuitry for storing 824,and/or circuitry for detecting 826. In other aspects, the circuitry 820is integrated with the processor 804.

Example Aspects

In addition to the various aspects described above, specificcombinations of aspects are within the scope of the disclosure, some ofwhich are detailed below:

Aspect 1. A method of wireless communication by a user equipment (UE),comprising: transmitting a first signal at a first transmission powerbased on time-averaged radio frequency (RF) exposure measurements over atime window; storing RF exposure information associated with the timewindow; detecting that an exception event associated with the UEoccurred; and transmitting a second signal at a second transmissionpower based at least in part on the stored RF exposure information inresponse to the detection of the event.

Aspect 2. The method of Aspect 1, wherein storing the RF exposureinformation comprises periodically storing the RF exposure information.

Aspect 3. The method according to any one of Aspects 1 or 2, whereinstoring the RF exposure information comprises storing the RF exposureinformation in a memory resistant to corruption from the exceptionevent.

Aspect 4. The method according to any one of Aspects 1-3, wherein:storing the RF exposure information comprises: storing the RF exposureinformation with a timestamp corresponding to when a most recenttime-averaged RF exposure measurement is generated, and obtaining thetimestamp from a counter resistant to the exception event; andtransmitting the second signal comprises transmitting the second signalat the second transmission power based at least in part on the stored RFexposure information in response to a determination that the timestampof the RF exposure information is within the time window.

Aspect 5. The method according to any of Aspects 1-4, wherein storingthe RF exposure information comprises storing the RF exposureinformation with a check value including a remainder in a cyclicredundancy check (CRC) of the RF exposure information.

Aspect 6. The method of Aspect 5, wherein transmitting the second signalcomprises transmitting the second signal at the second transmissionpower based on supplementing time-averaged RF exposure measurements fora current time window with the stored RF exposure information inresponse to a determination that the CRC of the RF exposure informationmatches the check value.

Aspect 7. The method according to any one of Aspects 1-6, whereintransmitting the second signal comprises transmitting the second signalat the second transmission power based on supplementing time-averaged RFexposure measurements with the stored RF exposure information.

Aspect 8. The method of Aspect 7, wherein transmitting the second signalcomprises transmitting the second signal at the second transmissionpower based at least in part on the stored RF exposure information whenat least one RF exposure measurement is missing from a current timewindow.

Aspect 9. The method according to any one of Aspects 1-8, wherein the RFexposure information includes a sum of the time-averaged RF exposuremeasurements or separate values for each of the time-averaged RFexposure measurements.

Aspect 10. The method according to any one of Aspects 1-9, wherein theexception event includes at least one of an error, a reset, a crash, ora reboot affecting an operation of the UE or a modem used intransmitting the first and second signals.

Aspect 11. The method according to any one of Aspects 1-10, wherein thetime-averaged RF exposure measurements comprise at least one of atime-averaged specific absorption rate (SAR) or a time-averaged powerdensity (PD).

Aspect 12. The method according to any one of Aspects 1-11, wherein thetransmitting the second signal is based on a determination of a type ofthe exception event.

Aspect 13. An apparatus for wireless communication, comprising: atransmitter configured to transmit a first signal at a firsttransmission power based on time-averaged radio frequency (RF) exposuremeasurements over a time window; a memory; and a processor coupled tothe memory, the processor and the memory being configured to: store RFexposure information associated with the time window, and detect that anexception event associated with the apparatus occurred; wherein thetransmitter is further configured to transmit a second signal at asecond transmission power based at least in part on the stored RFexposure information in response to the detection of the event.

Aspect 14. The apparatus of Aspect 13, further comprising a modemcoupled to the transmitter and the processor, the modem being configuredto provide, to the transmitter, instructions on the first transmissionpower and the second transmission power.

Aspect 15. The apparatus according to any one of Aspects 13 or 14,wherein the processor and the memory are further configured toperiodically store the RF exposure information.

Aspect 16. The apparatus according to any one of Aspects 13-15, whereinthe memory is resistant to corruption from the exception event.

Aspect 17. The apparatus according to any one of Aspects 13-16, furthercomprising a counter configured to provide a timestamp and resistant tothe exception event, wherein: the processor and the memory are furtherconfigured to: obtain the timestamp from the counter, and store the RFexposure information with the timestamp corresponding to when a mostrecent time-averaged RF exposure measurement is generated; and thetransmitter is further configured to transmit the second signal at thesecond transmission power based at least in part on the stored RFexposure information in response to a determination that the timestampof the RF exposure information is within a current time window.

Aspect 18. The apparatus according to any one of Aspects 13-17, furthercomprising a power management integrated circuit (PMIC), wherein thecounter is integrated with the PMIC.

Aspect 19. The apparatus according to any one of Aspects 13-18, whereinthe processor and the memory are further configured to store the RFexposure information with a check value including a remainder in acyclic redundancy check (CRC) of the RF exposure information.

Aspect 20. The apparatus of Aspect 19, wherein the transmitter isfurther configured to transmit the second signal at the secondtransmission power based on supplementing time-averaged RF exposuremeasurements for a current time window with the stored RF exposureinformation in response to a determination that the CRC of the RFexposure information matches the check value.

Aspect 21. The apparatus according to any one of Aspects 13-20, whereinthe transmitter is further configured to transmit the second signal atthe second transmission power based on supplementing time-averaged RFexposure measurements with the stored RF exposure information.

Aspect 22. The apparatus of Aspect 21, wherein the transmitter isfurther configured to transmit the second signal at the secondtransmission power based at least in part on the stored RF exposureinformation when at least one RF exposure measurement is missing fromthe time window.

Aspect 23. The apparatus according to any one of Aspects 13-22, whereinthe RF exposure information includes a sum of the time-averaged RFexposure measurements or separate values for each of the time-averagedRF exposure measurements.

Aspect 24. The apparatus according to any one of Aspects 13-23, whereinthe exception event includes at least one of an error, a reset, a crash,or a reboot affecting an operation of the apparatus or a modem used intransmitting the first and second signals.

Aspect 25. The apparatus according to any one of Aspects 13-24, whereinthe time-averaged RF exposure measurements comprise at least one of atime-averaged specific absorption rate (SAR) or a time-averaged powerdensity (PD).

Aspect 26. The apparatus of Aspect 13 configured to perform the methodof any of Aspects 1 through 12.

Aspect 27. An apparatus for wireless communication, comprising: meansfor transmitting a first signal at a first transmission power based ontime-averaged radio frequency (RF) exposure measurements over a timewindow; means for storing RF exposure information associated with thetime window; means for detecting that an exception event associated withthe apparatus occurred; and means for transmitting a second signal at asecond transmission power based at least in part on the stored RFexposure information in response to the detection of the event.

Aspect 28. The apparatus of Aspect 27, further comprising means forgenerating a timestamp, the means for generating the timestamp beingresistant to the exception event, wherein: the means for storing the RFexposure information comprises: means for obtaining the timestamp fromthe means for generating the timestamp, means for storing the RFexposure information with the timestamp corresponding to when a mostrecent time-averaged RF exposure measurement is generated; and the meansfor transmitting the second signal comprises means for transmitting thesecond signal at the second transmission power based at least in part onthe stored RF exposure information if the timestamp of the RF exposureinformation is within the time window.

Aspect 29. The apparatus of Aspect 27 comprising means for performingthe method of any one of Aspects 1 through 13.

Aspect 30. A computer-readable medium storing computer-executable codethereon for wireless communications that, when executed by at least oneprocessor, cause an apparatus to perform the method of any one ofAspects 1 through 12.

Aspect 31. The method according to any one of Aspects 1-12, wherein thetransmitting the second signal at the second transmission power is basedon a determination of a type of the exception event.

Aspect 32. The method according to any one of Aspects 1-12, wherein thetransmitting the second signal at the second transmission power is basedon a determination that transmission from the UE ceased during a portionof time corresponding to the exception event.

Aspect 33. The apparatus according to any one of Aspects 13-26, whereinthe processor and the memory are configured to determine a type of theexception event, and wherein the transmitter is configured to transmitthe second signal at the second transmission power based on thedetermination.

Aspect 34. The apparatus according to any one of Aspects 13-26, whereinthe processor and the memory are configured to determine thattransmission from the UE ceased during a portion of time correspondingto the exception event, and wherein the transmitter is configured totransmit the second signal at the second transmission power based on thedetermination.

Aspect 35. A method of wireless communication by a user equipment (UE),comprising: transmitting a first signal at a first transmission powerbased on time-averaged radio frequency (RF) exposure measurements over atime window; storing RF exposure information associated with the timewindow; detecting that an exception event associated with the UEoccurred; determining that a timestamp corresponding to a most recenttime-averaged RF exposure measurement is not within a current timewindow or determining that a check value does not pass a cyclicredundancy check (CRC) of the RF exposure information; and transmittinga second signal at a second transmission power in a failsafe mode basedon the determining.

Aspect 36. The method of Aspect 35, comprising obtaining the timestampfrom a counter resistant to the exception event.

Aspect 37. The method according to any one of Aspects 35 or 36, whereinthe second transmission power is determined based on a transmissionpower or exposure being at a maximum over the duration of a priorportion of the current time window.

Aspect 38. The method according to any one of Aspects 35-37, whereintime-averaged RF exposure measurements for the current time window arenot supplemented with the stored RF exposure information in the failsafemode.

Aspect 39. An apparatus for wireless communication, comprising: atransmitter configured to transmit a first signal at a firsttransmission power based on time-averaged radio frequency (RF) exposuremeasurements over a time window; a memory; and a processor coupled tothe memory, the processor and the memory being configured to: store RFexposure information associated with the time window, detect that anexception event associated with the apparatus occurred, and determinethat a timestamp corresponding to a most recent time-averaged RFexposure measurement is not within a current time window or determinethat a check value does not pass a cyclic redundancy check (CRC) of theRF exposure information; wherein the transmitter is further configuredto transmit a second signal at a second transmission power in a failsafemode based on the determination.

Aspect 40. An apparatus for wireless communication, comprising: meansfor transmitting a first signal at a first transmission power based ontime-averaged radio frequency (RF) exposure measurements over a timewindow; means for storing RF exposure information associated with thetime window; means for detecting that an exception event associated withthe UE occurred; means for determining that a timestamp corresponding toa most recent time-averaged RF exposure measurement is not within acurrent time window or means for determining that a check value does notpass a cyclic redundancy check (CRC) of the RF exposure information; andmeans for transmitting a second signal at a second transmission power ina failsafe mode based on the determining.

The techniques described herein may be used for various wirelesscommunication technologies, such as NR (e.g., 5G NR), 3GPP Long TermEvolution (LTE), LTE-Advanced (LTE-A), code division multiple access(CDMA), time division multiple access (TDMA), frequency divisionmultiple access (FDMA), orthogonal frequency division multiple access(OFDMA), single-carrier frequency division multiple access (SC-FDMA),time division synchronous code division multiple access (TD-SCDMA), andother networks. The terms “network” and “system” are often usedinterchangeably. A CDMA network may implement a radio technology such asUniversal Terrestrial Radio Access (UTRA), cdma2000, etc. UTRA includesWideband CDMA (WCDMA) and other variants of CDMA. cdma2000 coversIS-2000, IS-95 and IS-856 standards. A TDMA network may implement aradio technology such as Global System for Mobile Communications (GSM).An OFDMA network may implement a radio technology such as NR (e.g. 5GRA), Evolved UTRA (E-UTRA), Ultra Mobile Broadband (UMB), IEEE 802.11(Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Flash-OFDMA, etc. UTRA andE-UTRA are part of Universal Mobile Telecommunication System (UMTS). LTEand LTE-A are releases of UMTS that use E-UTRA. UTRA, E-UTRA, UMTS, LTE,LTE-A and GSM are described in documents from an organization named “3rdGeneration Partnership Project” (3GPP). cdma2000 and UMB are describedin documents from an organization named “3rd Generation PartnershipProject 2” (3GPP2). NR is an emerging wireless communications technologyunder development.

In 3GPP, the term “cell” can refer to a coverage area of a Node B (NB)and/or a NB subsystem serving this coverage area, depending on thecontext in which the term is used. In NR systems, the term “cell” andBS, next generation NodeB (gNB or gNodeB), access point (AP),distributed unit (DU), carrier, or transmission reception point (TRP)may be used interchangeably. A BS may provide communication coverage fora macro cell, a pico cell, a femto cell, and/or other types of cells,and/or may be configured as a CPE. A macro cell may cover a relativelylarge geographic area (e.g., several kilometers in radius) and may allowunrestricted access by UEs with service subscription. A pico cell maycover a relatively small geographic area and may allow unrestrictedaccess by UEs with service subscription. A femto cell may cover arelatively small geographic area (e.g., a home) and may allow restrictedaccess by UEs having an association with the femto cell (e.g., UEs in aClosed Subscriber Group (CSG), UEs for users in the home, etc.). A BSfor a macro cell may be referred to as a macro BS. A BS for a pico cellmay be referred to as a pico BS. A BS for a femto cell may be referredto as a femto BS or a home BS.

A UE may also be referred to and/or configured as a mobile station, aterminal, an access terminal, a subscriber unit, a station, a CPE, acellular phone, a smart phone, a personal digital assistant (PDA), awireless modem, a wireless communication device, a handheld device, alaptop computer, a cordless phone, a wireless local loop (WLL) station,a tablet computer, a camera, a gaming device, a netbook, a smartbook, anultrabook, an appliance, a medical device or medical equipment, abiometric sensor/device, a wearable device such as a smart watch, smartclothing, smart glasses, a smart wrist band, smart jewelry (e.g., asmart ring, a smart bracelet, etc.), an entertainment device (e.g., amusic device, a video device, a satellite radio, etc.), a vehicularcomponent or sensor, a smart meter/sensor, industrial manufacturingequipment, a global positioning system device, or any other suitabledevice that is configured to communicate via a wireless or wired medium.Some UEs may be considered machine-type communication (MTC) devices orevolved MTC (eMTC) devices. MTC and eMTC UEs include, for example,robots, drones, remote devices, sensors, meters, monitors, locationtags, etc., that may communicate with a BS, another device (e.g., remotedevice), or some other entity. A wireless node may provide, for example,connectivity for or to a network (e.g., a wide area network such asInternet or a cellular network) via a wired or wireless communicationlink. Some UEs may be considered Internet-of-Things (IoT) devices, whichmay be narrowband IoT (NB-IoT) devices.

In some examples, access to the air interface may be scheduled. Ascheduling entity (e.g., a BS) allocates resources for communicationamong some or all devices and equipment within its service area or cell.The scheduling entity may be responsible for scheduling, assigning,reconfiguring, and releasing resources for one or more subordinateentities. That is, for scheduled communication, subordinate entitiesutilize resources allocated by the scheduling entity. Base stations arenot the only entities that may function as a scheduling entity. In someexamples, a UE may function as a scheduling entity and may scheduleresources for one or more subordinate entities (e.g., one or more otherUEs), and the other UEs may utilize the resources scheduled by the UEfor wireless communication. In some examples, a UE may function as ascheduling entity in a peer-to-peer (P2P) network, and/or in a meshnetwork. In a mesh network example, UEs may communicate directly withone another in addition to communicating with a scheduling entity.

The methods disclosed herein comprise one or more steps or actions forachieving the methods. The method steps and/or actions may beinterchanged with one another without departing from the scope of theclaims. In other words, unless a specific order of steps or actions isspecified, the order and/or use of specific steps and/or actions may bemodified without departing from the scope of the claims.

As used herein, a phrase referring to “at least one of” a list of itemsrefers to any combination of those items, including single members. Asan example, “at least one of: a, b, or c” is intended to cover a, b, c,a-b, a-c, b-c, and a-b-c, as well as any combination with multiples ofthe same element (e.g., a-a, a-a-a, a-a-b, a-a-c, a-b-b, a-c-c, b-b,b-b-b, b-b-c, c-c, and c-c-c or any other ordering of a, b, and c).

As used herein, the term “determining” encompasses a wide variety ofactions. For example, “determining” may include calculating, computing,processing, deriving, investigating, looking up (e.g., looking up in atable, a database or another data structure), ascertaining and the like.Also, “determining” may include receiving (e.g., receiving information),accessing (e.g., accessing data in a memory) and the like. Also,“determining” may include resolving, selecting, choosing, establishing,and the like.

The previous description is provided to enable any person skilled in theart to practice the various aspects described herein. Variousmodifications to these aspects will be readily apparent to those skilledin the art, and the generic principles defined herein may be applied toother aspects. Thus, the claims are not intended to be limited to theaspects shown herein, but is to be accorded the full scope consistentwith the language of the claims, wherein reference to an element in thesingular is not intended to mean “one and only one” unless specificallyso stated, but rather “one or more.” Unless specifically statedotherwise, the term “some” refers to one or more. All structural andfunctional equivalents to the elements of the various aspects describedthroughout this disclosure that are known or later come to be known tothose of ordinary skill in the art are expressly incorporated herein byreference and are intended to be encompassed by the claims. Moreover,nothing disclosed herein is intended to be dedicated to the publicregardless of whether such disclosure is explicitly recited in theclaims. No claim element is to be construed under the provisions of 35U.S.C. § 112(f) unless the element is expressly recited using the phrase“means for” or, in the case of a method claim, the element is recitedusing the phrase “step for.”

The various operations of methods described above may be performed byany suitable means capable of performing the corresponding functions.The means may include various hardware and/or software component(s)and/or module(s), including, but not limited to a circuit, anapplication specific integrated circuit (ASIC), or processor. Generally,where there are operations illustrated in figures, those operations mayhave corresponding counterpart means-plus-function components withsimilar numbering.

The various illustrative logical blocks, modules and circuits describedin connection with the present disclosure may be implemented orperformed with a general purpose processor, a digital signal processor(DSP), an application specific integrated circuit (ASIC), a fieldprogrammable gate array (FPGA) or other programmable logic device (PLD),discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general-purpose processor may be a microprocessor, but in thealternative, the processor may be any commercially available processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

If implemented in hardware, an example hardware configuration maycomprise a processing system in a wireless node. The processing systemmay be implemented with a bus architecture. The bus may include anynumber of interconnecting buses and bridges depending on the specificapplication of the processing system and the overall design constraints.The bus may link together various circuits including a processor,machine-readable media, and a bus interface. The bus interface may beused to connect a network adapter, among other things, to the processingsystem via the bus. The network adapter may be used to implement thesignal processing functions of the PHY layer. In the case of a userterminal (see FIG. 1 ), a user interface (e.g., keypad, display, mouse,joystick, etc.) may also be connected to the bus. The bus may also linkvarious other circuits such as timing sources, peripherals, voltageregulators, power management circuits, and the like, which are wellknown in the art, and therefore, will not be described any further. Theprocessor may be implemented with one or more general-purpose and/orspecial-purpose processors. Examples include microprocessors,microcontrollers, DSP processors, and other circuitry that can executesoftware. Those skilled in the art will recognize how best to implementthe described functionality for the processing system depending on theparticular application and the overall design constraints imposed on theoverall system.

If implemented in software, the functions may be stored or transmittedover as one or more instructions or code on a computer-readable medium.Software shall be construed broadly to mean instructions, data, or anycombination thereof, whether referred to as software, firmware,middleware, microcode, hardware description language, or otherwise.Computer-readable media include both computer storage media andcommunication media including any medium that facilitates transfer of acomputer program from one place to another. The processor may beresponsible for managing the bus and general processing, including theexecution of software modules stored on the machine-readable storagemedia. A computer-readable storage medium may be coupled to a processorsuch that the processor can read information from, and write informationto, the storage medium. In the alternative, the storage medium may beintegral to the processor. By way of example, the machine-readable mediamay include a transmission line, a carrier wave modulated by data,and/or a computer-readable storage medium with instructions storedthereon separate from the wireless node, all of which may be accessed bythe processor through the bus interface. Alternatively, or in addition,the machine-readable media, or any portion thereof, may be integratedinto the processor, such as the case may be with cache and/or generalregister files. Examples of machine-readable storage media may include,by way of example, RAM (Random Access Memory), flash memory, ROM (ReadOnly Memory), PROM (Programmable Read-Only Memory), EPROM (ErasableProgrammable Read-Only Memory), EEPROM (Electrically ErasableProgrammable Read-Only Memory), registers, magnetic disks, opticaldisks, hard drives, or any other suitable storage medium, or anycombination thereof. The machine-readable media may be embodied in acomputer-program product.

A software module may comprise a single instruction, or manyinstructions, and may be distributed over several different codesegments, among different programs, and across multiple storage media.The computer-readable media may comprise a number of software modules.The software modules include instructions that, when executed by anapparatus such as a processor, cause the processing system to performvarious functions. The software modules may include a transmissionmodule and a receiving module. Each software module may reside in asingle storage device or be distributed across multiple storage devices.By way of example, a software module may be loaded into RAM from a harddrive when a triggering event occurs. During execution of the softwaremodule, the processor may load some of the instructions into cache toincrease access speed. One or more cache lines may then be loaded into ageneral register file for execution by the processor. When referring tothe functionality of a software module below, it will be understood thatsuch functionality is implemented by the processor when executinginstructions from that software module.

Also, any connection is properly termed a computer-readable medium. Forexample, if the software is transmitted from a website, server, or otherremote source using a coaxial cable, fiber optic cable, twisted pair,digital subscriber line (DSL), or wireless technologies such as infrared(IR), radio, and microwave, then the coaxial cable, fiber optic cable,twisted pair, DSL, or wireless technologies such as infrared, radio, andmicrowave are included in the definition of medium. Disk and disc, asused herein, include compact disc (CD), laser disc, optical disc,digital versatile disc (DVD), floppy disk, and Blu-ray® disc where disksusually reproduce data magnetically, while discs reproduce dataoptically with lasers. Thus, in some aspects computer-readable media maycomprise non-transitory computer-readable media (e.g., tangible media).In addition, for other aspects computer-readable media may comprisetransitory computer-readable media (e.g., a signal). Combinations of theabove should also be included within the scope of computer-readablemedia.

Thus, certain aspects may comprise a computer program product forperforming the operations presented herein. For example, such a computerprogram product may comprise a computer-readable medium havinginstructions stored (and/or encoded) thereon, the instructions beingexecutable by one or more processors to perform the operations describedherein, for example, instructions for performing the operationsdescribed herein and illustrated in FIG. 4 .

Further, it should be appreciated that modules and/or other appropriatemeans for performing the methods and techniques described herein can bedownloaded and/or otherwise obtained by a user terminal and/or basestation as applicable. For example, such a device can be coupled to aserver to facilitate the transfer of means for performing the methodsdescribed herein. Alternatively, various methods described herein can beprovided via storage means (e.g., RAM, ROM, a physical storage mediumsuch as a compact disc (CD) or floppy disk, etc.), such that a userterminal and/or base station can obtain the various methods uponcoupling or providing the storage means to the device. Moreover, anyother suitable technique for providing the methods and techniquesdescribed herein to a device can be utilized.

It is to be understood that the claims are not limited to the preciseconfiguration and components illustrated above. Various modifications,changes, and variations may be made in the arrangement, operation, anddetails of the methods and apparatus described above without departingfrom the scope of the claims.

The invention claimed is:
 1. A method of wireless communication by awireless device, comprising: transmitting a first signal at a firsttransmission power based on time-averaged radio frequency (RF) exposuremeasurements over a time window; storing RF exposure informationassociated with the time window; detecting that an exception eventassociated with the wireless device occurred; and transmitting a secondsignal at a second transmission power based at least in part on thestored RF exposure information in response to the detection of theexception event and in response to a determination that the RF exposureinformation passes a reliability check.
 2. The method of claim 1,wherein storing the RF exposure information comprises periodicallystoring the RF exposure information.
 3. The method of claim 1, whereinstoring the RF exposure information comprises storing the RF exposureinformation in a memory resistant to corruption from the exceptionevent.
 4. The method of claim 1, wherein: storing the RF exposureinformation comprises: storing the RF exposure information with atimestamp corresponding to when a most recent time-averaged RF exposuremeasurement is generated, and obtaining the timestamp from a counterresistant to the exception event; and transmitting the second signalcomprises transmitting the second signal at the second transmissionpower based at least in part on the stored RF exposure information inresponse to a determination that the timestamp of the RF exposureinformation is within a current time window.
 5. The method of claim 1,wherein storing the RF exposure information comprises storing the RFexposure information with a check value including a remainder in acyclic redundancy check (CRC) of the RF exposure information.
 6. Themethod of claim 5, wherein transmitting the second signal comprisestransmitting the second signal at the second transmission power based onsupplementing time-averaged RF exposure measurements for a current timewindow with the stored RF exposure information in response to adetermination that the CRC of the RF exposure information matches thecheck value, wherein the passed reliability check includes when the CRCof the RF exposure information matches the check value.
 7. The method ofclaim 1, wherein transmitting the second signal comprises transmittingthe second signal at the second transmission power based onsupplementing time-averaged RF exposure measurements with the stored RFexposure information.
 8. The method of claim 7, wherein transmitting thesecond signal comprises transmitting the second signal at the secondtransmission power based at least in part on the stored RF exposureinformation when at least one RF exposure measurement is missing from acurrent time window.
 9. The method of claim 1, wherein the RF exposureinformation includes a sum of the time-averaged RF exposure measurementsor separate values for each of the time-averaged RF exposuremeasurements.
 10. The method of claim 1, wherein the exception eventincludes at least one of an error, a reset, a crash, or a rebootaffecting an operation of the wireless device or a modem used intransmitting the first and second signals.
 11. The method of claim 1,wherein the time-averaged RF exposure measurements comprise at least oneof a time-averaged specific absorption rate (SAR) or a time-averagedpower density (PD).
 12. The method of claim 1, wherein the transmittingthe second signal is based on a determination of a type of the exceptionevent.
 13. An apparatus for wireless communication, comprising: atransmitter configured to transmit a first signal at a firsttransmission power based on time-averaged radio frequency (RF) exposuremeasurements over a time window; a memory; and a processor coupled tothe memory, the processor and the memory being configured to: store RFexposure information associated with the time window, and detect that anexception event associated with the apparatus occurred; wherein thetransmitter is further configured to transmit a second signal at asecond transmission power based at least in part on the stored RFexposure information in response to the detection of the exception eventand in response to a determination that the RF exposure informationpasses a reliability check.
 14. The apparatus of claim 13, furthercomprising a modem coupled to the transmitter and the processor, themodem being configured to provide, to the transmitter, instructions onthe first transmission power and the second transmission power.
 15. Theapparatus of claim 13, wherein the processor and the memory are furtherconfigured to periodically store the RF exposure information.
 16. Theapparatus of claim 13, wherein the memory is resistant to corruptionfrom the exception event.
 17. The apparatus of claim 13, furthercomprising a counter configured to provide a timestamp and resistant tothe exception event, wherein: the processor and the memory are furtherconfigured to: obtain the timestamp from the counter, and store the RFexposure information with the timestamp corresponding to when a mostrecent time-averaged RF exposure measurement is generated; and thetransmitter is further configured to transmit the second signal at thesecond transmission power based at least in part on the stored RFexposure information in response to a determination that the timestampof the RF exposure information is within a current time window.
 18. Theapparatus of claim 17, further comprising a power management integratedcircuit (PMIC), wherein the counter is integrated with the PMIC.
 19. Theapparatus of claim 13, wherein the processor and the memory are furtherconfigured to store the RF exposure information with a check valueincluding a remainder in a cyclic redundancy check (CRC) of the RFexposure information.
 20. The apparatus of claim 19, wherein thetransmitter is further configured to transmit the second signal at thesecond transmission power based on supplementing time-averaged RFexposure measurements for a current time window with the stored RFexposure information in response to a determination that the CRC of theRF exposure information matches the check value, wherein the passedreliability check includes when the CRC of the RF exposure informationmatches the check value.
 21. The apparatus of claim 13, wherein thetransmitter is further configured to transmit the second signal at thesecond transmission power based on supplementing time-averaged RFexposure measurements with the stored RF exposure information.
 22. Theapparatus of claim 21, wherein the transmitter is further configured totransmit the second signal at the second transmission power based atleast in part on the stored RF exposure information when at least one RFexposure measurement is missing from the time window.
 23. The apparatusof claim 13, wherein the RF exposure information includes a sum of thetime-averaged RF exposure measurements or separate values for each ofthe time-averaged RF exposure measurements.
 24. The apparatus of claim13, wherein the exception event includes at least one of an error, areset, a crash, or a reboot affecting an operation of the apparatus or amodem used in transmitting the first and second signals, and wherein thetime-averaged RF exposure measurements comprise at least one of atime-averaged specific absorption rate (SAR) or a time-averaged powerdensity (PD).
 25. The apparatus of claim 13, wherein the processor andthe memory are configured to determine that transmission from theapparatus ceased during a portion of time corresponding to the exceptionevent, and wherein the transmitter is configured to transmit the secondsignal at the second transmission power based on the determination. 26.A method of wireless communication by a user equipment (UE), comprising:transmitting a first signal at a first transmission power based ontime-averaged radio frequency (RF) exposure measurements over a timewindow; storing RF exposure information associated with the time window;detecting that an exception event associated with the UE occurred;determining that a timestamp corresponding to a most recenttime-averaged RF exposure measurement is not within a current timewindow or determining that a check value does not pass a cyclicredundancy check (CRC) of the RF exposure information; and transmittinga second signal at a second transmission power in a failsafe mode basedon the determining.
 27. The method of claim 26, comprising obtaining thetimestamp from a counter resistant to the exception event.
 28. Themethod of claim 26, wherein the second transmission power is determinedbased on a transmission power or exposure being at a maximum over aprior portion of the current time window.
 29. The method of claim 26,wherein time-averaged RF exposure measurements for the current timewindow are not supplemented with the stored RF exposure information inthe failsafe mode.
 30. An apparatus for wireless communication,comprising: a transmitter configured to transmit a first signal at afirst transmission power based on time-averaged radio frequency (RF)exposure measurements over a time window; a memory; and a processorcoupled to the memory, the processor and the memory being configured to:store RF exposure information associated with the time window, detectthat an exception event associated with the wireless device occurred,and determine the RF exposure information is outside a current timewindow or determine the RF exposure information fails a reliabilitycheck; wherein the transmitter is further configured transmit a secondsignal at a second transmission power in a failsafe mode based on thedetermination.